1
Further considerations on objectives for PHYs running over point-to-point DWDM systems
Peter Stassar (Huawei), Pete Anslow (Ciena) IEEE 802.3 Beyond 10 km Optical PHYs Study Group IEEE 802.3 Plenary Meeting, Rosemont, 5 – 9 March 2018
2
Supporters Steve Trowbridge, Nokia
3
Introduction In this presentation reference is made to the following presentations
provided to the b10k meeting in Geneva, January 2018:
http://www.ieee802.org/3/B10K/public/18_01/anslow_b10k_01_0118
.pdf defining 6 different optical link types
http://www.ieee802.org/3/B10K/public/18_01/stassar_b10k_01_011
8.pdf proving further considerations on objectives for PHYs
running over point-to-point DWDM systems using the 6 different
optical link types as a starting point.
http://www.ieee802.org/3/B10K/public/18_01/nicholl_b10k_01a_011
8.pdf suggesting potential strawman language of a “DWDM PHY”
objective
In this presentation further considerations are provided.
http://www.ieee802.org/3/B10K/public/17_11/stassar_b10k_01a_1117.pdfhttp://www.ieee802.org/3/B10K/public/17_11/stassar_b10k_01a_1117.pdfhttp://www.ieee802.org/3/B10K/public/17_11/stassar_b10k_01a_1117.pdfhttp://www.ieee802.org/3/B10K/public/17_11/stassar_b10k_01a_1117.pdfhttp://www.ieee802.org/3/B10K/public/18_01/stassar_b10k_01_0118.pdfhttp://www.ieee802.org/3/B10K/public/18_01/stassar_b10k_01_0118.pdfhttp://www.ieee802.org/3/B10K/public/17_11/stassar_b10k_01a_1117.pdfhttp://www.ieee802.org/3/B10K/public/18_01/nicholl_b10k_01a_0118.pdfhttp://www.ieee802.org/3/B10K/public/18_01/nicholl_b10k_01a_0118.pdf
4
Recap on link type 3
Optical Tx
Optical Rx Example 100GBASE-ER4
Is WDM link.
Can be CWDM (20nm spaced) or DWDM (frequency spaced)
CWDM examples: 40GBASE-LR4/ER4, 200GBASE-FR4
DWDM examples: 100GBASE-LR4, 200GBASE-LR4, 400GBASE-
FR8/LR8
5
Recap link type 4
Is WDM network between multiple Tx and multiple Rx, each in
point-to-point link via the network
Black link between T and R is passive, no optical amplifiers.
Can be CWDM (20nm spaced) or DWDM (frequency spaced, e.g.
800 GHz)
CWDM examples in ITU-T G.695
DWDM examples in ITU-T G.698.1
Optical Tx Optical Rx
Optical Tx Optical Rx
Optical Tx Optical Rx
Example G.698.1
.
.
.
.
.
.
T R
6
Recap on link type 5 versus link type 6
The only difference between link types 5 and 6 is the presence of
OADMs.
From a specification methodology (black link) point of view there
is NO difference between 5 and 6.
Link type 5 requirements for OSNR @ R and “tunnel” width (max
spectral excursion) may be less stringent than for type 6.
In both cases the link performance may be heavily determined by
non-linear effects inside the black link
Optical Tx Optical Rx
Optical Tx Optical Rx
Optical Tx Optical Rx
.
.
.
.
.
.
T R
Example G.698.2
Optical Tx Optical Rx
Optical Tx Optical Rx
Optical Tx Optical Rx
.
.
.
.
.
.
OADM
Opt
ical
Tx
Opt
ical
Rx
R T
Example simplified G.698.2
7
Back to Link type 5
Example simplified G.698.2
Optical Tx Optical Rx
Optical Tx Optical Rx
Optical Tx Optical Rx
.
.
.
.
.
.
T R
The proposal in nicholl_b10k_01a_0118 is equivalent to adopt an
objective for a PMD covering link type 5 in anslow_b10k_01_0118.
Also the following is stated in nicholl_b10k_01a_0118
“No need to define the details of the point-to-point DWDM system
itself.”
This implies adoption of a black link specification methodology between
T and R.
More on black link later in this presentation
8
ITU-T SG15 & IEEE 802 workshop 27 Jan 2018
Suggestion from the joint workshop between IEEE 802.3 and ITU-T SG15,
held on 27 January 2018, in particular Session 1 “New High-Speed and
Long Reach Optical Interfaces”, as noted in https://www.itu.int/en/ITU-
T/Workshops-and-Seminars/20180127/Documents/Outcomes%20-
%20Building%20Tomorrow%20Networks-Final.pdf:
IEEE 802.3 B10k SG should weigh the implications of moving away from
a comprehensive “plug -and -play” specification to one where the detail
of how to engineer the “black link” to meet the transfer specifications is
not specified by the standard.
https://www.itu.int/en/ITU-T/Workshops-and-Seminars/20180127/Documents/Outcomes%20-%20Building%20Tomorrow%20Networks-Final.pdfhttps://www.itu.int/en/ITU-T/Workshops-and-Seminars/20180127/Documents/Outcomes%20-%20Building%20Tomorrow%20Networks-Final.pdfhttps://www.itu.int/en/ITU-T/Workshops-and-Seminars/20180127/Documents/Outcomes%20-%20Building%20Tomorrow%20Networks-Final.pdf
9
Impact of adopting black link methodology
The black link is intentionally “black”, no details are provided on
constraints to operate a link or how to construct a link towards meeting
overall performance objectives.
Introduction of one or more optical amplifiers inside “black link” between
T and R:
No longer loss limited system. OSNR at Rx input (R).
Introduction of non-linear impairments inside “black link”.
Non-linear interaction between the parallel channels inside “black link”
between T and R, depending heavily of the “nature” of the parallel
channels.
Hugely different link behaviour and “interaction”, e.g. in the case of 10G
NRZ amplitude modulated signals in parallel to 100G coherent signals.
10
Impact of adopting black link methodology One talks about a “black link provider” as the “entity” in control of the
performance of the link
Constructing a black DWDM link (even when it only contains a mux, one
optical amplifier, one fiber section and a demux) is a complete
engineering effort where one needs to take account of:
Manage amplifier gain tilt when loading the system from 1 or 2, to n
channels, because the performance of the link changes versus
number of loaded channels.
Avoiding transients (surges from amplifier due to changes in number
of channels)
Effectively managing the OA(s) in a black link requires a complete set
engineering set of decisions.
It’s impossible to cover all of this in a single specification.
Therefore some speak of “a room full of PhD’s”.
11
Example of non-linear behaviour
If the black link is not engineered well, the OSNR penalty runs off a cliff.
Source: ITU-T supplement G.Sup39
12
Summary
The benefit of using black link specification methodology is that it
allows the end user a lot of flexibility for a wide range of
applications:
In terms of distance, number of channels, nature of signals
carried across the DWDM link.
In ITU-T a black link spec is created on the basis of terms of
reference like “appropriate for 80 km distances, single span, no
OADMs, not precluding 120 km and 1 or 2 OADMs”.
Defining a DWDM (black) link spec for a very specific
configuration, e.g. only 80 km single span no OADMs, would
significantly narrow application space and thus broad market
potential.
13
Key question (workshop)
What are the implications of moving away from a
comprehensive “plug -and -play” specification to
one where the detail of how to engineer the
“black link” to meet the transfer specifications is
not specified by the standard?
14
Q & A?
15
Thanks
Further considerations on objectives for PHYs �running over point-to-point DWDM systems�SupportersIntroductionRecap on link type 3Recap link type 4Recap on link type 5 versus link type 6Back to Link type 5ITU-T SG15 & IEEE 802 workshop 27 Jan 2018Impact of adopting black link methodologyImpact of adopting black link methodologyExample of non-linear behaviourSummaryKey question (workshop)Q & A?Thanks
Top Related